Central nervous system serotonin and personality as variables contributing to excessive alcohol consumption in non-human primates

Anabolic androgenic steroid affects competitive behaviour, behavioural response to ethanol and brain serotonin levels

The present study investigated whether anabolic androgenic steroid (AAS) treatment (daily subcutaneous injections during 2 weeks with nandrolone decanoate; 15 mg/kg) affects competitive behaviour, and locomotor activity response to a sedative dose of ethanol (0.5 g ethanol/kg). In addition, levels of brain monoamines were assessed. The results showed that AAS treated animals exhibited enhanced dominant behaviour in the competition test compared to controls. The AAS groups' locomotor activity was not affected by ethanol in contrast to the controls who showed a sedative locomotor activity. AAS animals had significant lower levels of serotonin in basal forebrain and dorsal striatum compared to controls. These findings further strengthen the fact that AAS affects behaviour, as well as biochemical parameters. Based on previous studies and results from the present study, we hypothesize that AAS abuse may constitute a risk factor for disinhibitory behaviour, partly by affecting the serotonergic system.

Evolutionary underpinnings of excessive alcohol consumption

Given our close phylogenetic relatedness, non-human primates, in principle, could serve as an ideal model for alcoholism. Indeed, many studies in both humans and rhesus macaques show relationships between excessive alcohol consumption, aggression and serotonergic function, as measured by concentrations of the principal metabolite of serotonin, 5-hydroxyindoleacetic acid (5-HIAA) in the cerebrospinal fluid (CSF). An important behavioral predictor of excessive alcohol consumption in both humans and rhesus monkeys is the propensity toward impulsivity. Integrating behavioral and neuroendocrine data from captive and semi-free-ranging rhesus macaques, we posit that benefits derived from impulsive and aggressive behaviors in some contexts might contribute indirectly to the maintenance of traits involved in alcoholism and excessive alcohol intake.

Brain 5-HT receptor system in the stressed infant rat: implications for vulnerability to substance abuse

Clinical and epidemiological studies have found an association between aversive experiences early in life and an increased risk for depression, anxiety and substance abuse. In order to elucidate the mechanisms by which adverse life events are translated into behavioral and psychological abnormalities, we used a rat model to study the impact of chronic injection and 24 h maternal deprivation on the developing rat brain. Specifically, we investigated the regulation of molecules related to the 5-HT (5-HT) system and studied the effect of desipramine administration on animals that were maternally deprived (DEP) on day 13 of life compared with non-deprived animals. We found that maternal deprivation caused an enhanced corticosterone response to an acute stress. Maternally deprived animals also showed a decrease in corticosteroid receptors and an increase in 5-HT 1A and 1B receptors restricted to the CA1 region of the hippocampus. Desipramine prevented the maternal deprivation induced up-regulation of the 5-HT 1B receptor and the enhanced adrenocortical response observed in these animals. Interestingly, non-deprived animals receiving chronic injections showed a decrease in hippocampal 5-HT1B receptor mRNA. At 80 days of age, a group of animals that were treated as infants were given the option of drinking from two identical water bottles, one bottle contained tap water, while the second contained ethanol at increasing concentrations. Animals that received chronic injections during the newborn period consumed more alcohol than those that were not injected. On the other hand, maternal deprivation did not have an impact on alcohol consumption. Alcohol preference has implications to the organism since studies of drug self-administration in laboratory animals have shown that ethanol ingestion is positively related to the use of other drugs, principally opioids and psychostimulants. Our findings suggest that the quality and/or chronicity of early life stressors can influence the neurobiological substrates that may trigger and/or predispose individuals to substance abuse in adulthood.

Is long-term heavy alcohol consumption toxic for brain serotonergic neurons? Relationship between years of excessive alcohol consumption and serotonergic neurotransmission

The relationship between years of excessive alcohol consumption and central serotonergic neurotransmission, as assessed by the prolactin (PRL) response to D-fenfluramine, was investigated in 22 male alcohol-dependent subjects. A negative correlation was obtained, that is, the longer duration of excessive alcohol consumption the lower PRL response to D-fenfluramine. It is therefore suggested that long duration of excessive alcohol consumption in alcohol-dependent subjects causes a reduction in central serotonergic neurotransmission, possibly by a toxic effect of alcohol on serotonin neurons. The relationship between depressive and anxiety symptoms during on-going drinking and the PRL response to D-fenfluramine was also investigated. No such correlations were obtained, suggesting that reduction in central serotonergic neurotransmission does not pre-dispose to the development of depressive and anxiety symptoms, at least in relation to on-going drinking in alcohol-dependent subjects.

Initial ethanol exposure results in decreased heart rate variability in ethanol-naive rhesus monkeys

Ethanol's effects on heart rate variability may contribute to the increased cardiac disease and mortality observed in alcoholics. We assessed cardiac response to ethanol in seven previously ethanol-naive monkeys given a standard dose of ethanol, or saline. Ethanol exposure reduced cardiac signal complexity [mean+/-S.D. (ethanol: Hurst parameter=0.39+/-0.02; saline: Hurst parameter=0.32+/-0.06)] and increased the spectral exponent (ethanol: beta=1.36+/-0.35; saline: beta=1.12+/-0.35) when compared to saline, while heart rate itself was unaffected (saline: interbeat interval=303.57+/-24.57; ethanol: interbeat interval=308.14+/-20.45). Taken together with data that show autonomic disregulation in alcoholics, these findings provide further evidence of deleterious ethanol effects on cardiac signal dynamics.

A multiple schedule model of limited access drinking in the cynomolgus macaque

The present study reports on the development of a multiple schedule procedure of oral ethanol self-administration in cynomolgus macaques. Six adult cynomolgus macaques (four female, two male) were trained to self-administer ethanol and water under a 60 min, four-component multiple schedule of ethanol and water access with 1 g food pellets presented every 900 s (fixed-time 900 s). Water was available for the first and third 15 min components, ethanol in the second and fourth components. Total ethanol dose was stable at between 1-1.25 g/kg at ethanol concentration of 4%, 6% and 8%. Subsequently water was replaced with a sweetened drink (sugar-free Tang powder, General Foods). Ethanol and Tang were self-administered in similar volumes and both served as reinforcers compared with water. Acute pretreatment with 0.25 to 1.5 g/kg of intragastrically gavaged (i.g.) ethanol failed to alter ethanol or Tang self-administration significantly despite producing mean blood ethanol levels of up to 199 mg/dl when combined with self-administered ethanol. However, 1.0 g/kg i.g. ethanol administered for 15 consecutive days significantly decreased ethanol self-administration by 23%. The results suggest that ethanol self-administration under a multiple schedule is insensitive to alteration by acute ethanol pretreatment, but can be decreased by more prolonged chronic ethanol pretreatment.

From mice to men: what can we learn about personality from animal research?

The author explores the viability of a comparative approach to personality research. A review of the diverse animal-personality literature suggests that (a) most research uses trait constructs, focuses on variation within (vs. across) species, and uses either behavioral codings or trait ratings; (b) ratings are generally reliable and show some validity (7 parameters that could influence reliability and 4 challenges to validation are discussed); and (c) some dimensions emerge across species, but summaries are hindered by a lack of standard descriptors. Arguments for and against cross-species comparisons are discussed, and research guidelines are suggested. Finally, a research agenda guided by evolutionary and ecological principles is proposed. It is concluded that animal studies provide unique opportunities to examine biological, genetic, and environmental bases of personality and to study personality change, personality-health links, and personality perception.